1. Field of the Invention
This invention relates to a system that facilitates recovery of blowout preventer stacks, subsea trees and similar structures used in oil and gas drilling operations in a subsea environment. The blowout preventer stack connects to the subsea wellhead located on the ocean floor. These blowout preventer stacks are part of a pressure control system used in offshore oil and gas drilling operations to control unexpected well bore pressure spikes or "kicks" as they are commonly referred to in the industry.
The typical subsea blowout preventer stack has a plurality of blowout preventers positioned in a predetermined vertical arrangement or "stack" depending on well conditions and the preferences of the drilling contractor. Each blowout preventer has a vertical bore sized to allow passage of casing, drill pipe, drill bits and downhole tools. A typical subsea "stack" will include both ram-type and annular blowout preventers. Additionally, the stack will include a support frame to facilitate handling during deployment operations and as a support for other components including a control system, kill and choke lines and associated valves and piping.
The typical subsea blowout preventer stack is built and handled in two sections, a lower section known as the "main stack" and an upper section known as the "lower marine riser package." In normal operation, the blowout preventer stack is lowered to the ocean floor and retrieved to the surface using either the drilling riser or a purpose built tool for use with drill pipe. These blowout preventer stacks represent a considerable investment to the drilling contractor and it is important that a damaged stack be retrieved if at all possible. If a malfunction occurs that prevents retrieval of the stack in the usual manner, an emergency recovery system is needed. Most emergency recovery systems currently used require the deployment of special tools or grappling lines.
Problems associated with these current systems include difficulty in use depending on the extent of damage to the blowout preventer stack and causing additional damage to the blowout preventer stack during these recovery operations, especially when grappling lines are used. Similar problems occur during recovery of subsea trees.
2. Description of Related Art
U.S. Pat. No. 1,189,864 to J. C. Paulson shows a device for locating and raising sunken vessels, particularly submarines. The device requires either compressed air or manual manipulation by a person on the submarine for activation.
A submarine detection float is disclosed in U.S. Pat. No. 1,636,447 to T. L. Standish. This apparatus uses a hand wheel activated release mechanism to deploy a float with an air line for sending air to persons trapped in a submarine.
U.S. Pat. No. 1,696,053 to J. Pasini discloses an automatically released buoy when a ship sinks to aid in location and recovery of the sunken ship.
U.S. Pat. No. 2,594,702 to S. W. Woodard discloses a retrievable marine marker that utilizes a geophone activated by an explosion to release a locator buoy.
An apparatus for automatically releasing a submerged buoy after a predetermined period of submersion is shown in U.S. Pat. No. 2,722,019 to A. T. Brock.
U.S. Pat. No. 2,752,615 to L. L. Parker discloses a marker buoy for use in recovering missiles from under water. A water soluble tablet is used to activate the buoy release mechanism.